Method for producing melt of urea and biuret and system for producing such melt

Abstract

The present disclosure relates to a method and system for producing a melt comprising urea, biuret and a small amount of N-containing compounds produced during a urea condensation process, the method comprising the steps of: pumping the urea melt to one or more reactor vessels, each reactor vessel having a head space at its top and a bottom; the urea melt in the one or more reactor vessels is subjected to a heating process at a temperature of between 150 DEG C and 180 DEG C, during which heating process, the melt present in the reactor vessel is also subjected to a circulation process in and out of the one or more reactor vessels via a circulation loop arranged outside each of the reactor vessels, and wherein during formation of the melt, a gaseous by-product is produced, the gaseous by-product is discharged from the respective reactor vessel via the top of the respective reactor vessel; and removing the melt from the one or more reactor vessels via the bottom of the one or more reactor vessels.

Description

Technical Field

[0001] The present disclosure relates to methods and systems for producing melts of urea, biuret, and small amounts of N-containing compounds produced during the urea condensation process. Background Art

[0002] It is well known that when urea is heated at temperatures starting from 130 °C, it thermally decomposes to form condensation products, namely biuret. As the concentration of biuret increases and with increasing temperature, other urea pyrolysis products or urea condensation products such as triuret, cyanuric acid monoamide, cyanuric acid, etc. start to form. The higher the temperature, the faster the rate of conversion of urea to biuret.

[0003] US 4,540,820 discloses a method for preparing a composition that is particularly suitable for use as a raw material in the production of animal feed grade biuret by solid-state pyrolysis in a circulating furnace. The composition comprises by weight about 37% to about 25% urea, by weight about 45% to about 60% biuret, and by weight about 3% to about 20% cyanuric acid. Such a preparation method includes passing air or other non-reactive gas through a urea feedstock by bubbling at a rate of about 2 to about 10 cubic feet of gas per hour per pound of urea at a temperature of about 145 °C to about 165 °C for at least four hours, and then cooling and pulverizing the product.

[0004] EP 3 995 488 discloses a method for producing feed grade urea starting from a liquid urea melt, the method comprising treating the urea melt to promote the formation of biuret until the concentration of biuret is at least 3% by weight, and subjecting the biuret-containing melt thus obtained to a shaping method to obtain a granular urea product.

[0005] Now, an object of the present disclosure is to provide simple methods for producing a melt that contains urea, biuret, and relatively small amounts of by-products, i.e., "small amounts" of N-containing compounds, produced during the urea condensation process, without the need for additional purification steps and without any additional reactants, solvents, etc.

[0006] Another object of the present disclosure is to provide a method for producing such a melt that is suitable for further processing into a non-protein nitrogen (NPN) source, and more particularly for use as an animal feed grade additive for ruminants and cattle. Summary of the Invention

[0007] According to a first aspect of the present disclosure, there is disclosed a method for producing a melt comprising urea, biuret, and small amounts of N-containing compounds produced during the urea condensation process (hereinafter referred to as "melt comprising urea, biuret, and N-containing compounds"), the method comprising the following steps:

[0008] - Pump the urea melt into one or more reactor vessels, each reactor vessel having a headspace at its top and a bottom;

[0009] - Subject the urea melt in the one or more reactor vessels to a heating process at a temperature between 150 °C and 180 °C, wherein during the heating process, the urea melt is converted into a melt containing urea, biuret, and N - containing compounds;

[0010] - During the heating process, subject the melt present in the reactor vessels to a circulation process through a circulation loop arranged outside each of the reactor vessels and into and out of the one or more reactor vessels,

[0011] wherein during the formation of the melt containing urea, biuret, and N - containing compounds, gaseous by - products are generated, which are discharged from the respective reactor vessels through the tops of the respective reactor vessels, and - Remove the melt containing urea, biuret, and N - containing compounds from the one or more reactor vessels through the bottoms of the one or more reactor vessels.

[0012] The urea melt is liquid urea, optionally containing a minimal amount of water. The melting temperature of solid urea is between 130 °C and 133 °C, depending on the amount of water.

[0013] The advantage of the method according to the present disclosure is that it is a simple and rapid production method that can produce the melt disclosed above without using a catalyst and a solvent. During this production method, only a small amount of by - products are formed during the urea condensation process, generally less than 15 wt.%, more particularly N - containing compounds such as cyanuric acid amide, cyanuric acid, triuret, etc. Therefore, no further purification step is required before adding it as a feed supplement to ruminant feed. In addition, the circulation loop arranged outside the one or more reactor vessels enhances the mixing of the melt, contributing to mass transfer and the flashing of the liquid.

[0014]

[0015]

[0016]

[0017] In one embodiment of the method according to the present disclosure, the method is a batch method, and the residence time of the melt is between 40 minutes and 120 minutes, more particularly between 60 minutes and 90 minutes, which generally depends on the amount of melt present in the reactor vessels and the process conditions in the reactor vessels.

[0018]

[0019] ​​​​In another embodiment of the method according to the present disclosure, the method is a continuous method, and the residence time of the melt in one or more reactor vessels is between 40 minutes and 60 minutes, typically depending on the capacity / volume of the reactor vessels and the flow rate of the urea melt.

[0020] Considering known production methods, these residence times as described above are quite short.

[0021] In a possible embodiment of the method according to the present disclosure, the method further comprises the following steps:

[0022] - introducing a carrier gas into the melt in one or more reactor vessels, which carrier gas will then mix with gaseous

[0023] by-products to produce a gas mixture, the carrier gas being more particularly nitrogen, carbon dioxide, air or a mixture thereof bubbled in the respective reactor vessels using a gas distributor, and / or

[0024] or

[0025] - introducing a purge gas stream into the headspace of one or more reactor vessels, which purge gas stream will then mix with gaseous by-products to produce a gas mixture, the purge gas stream being more particularly a purge air stream;

[0026] - discharging the gas mixture from the respective reactor vessels via the top of the respective reactor vessels.

[0027] Introducing a carrier gas into the melt or a purge gas stream into the headspace of the respective reactor vessels to discharge the formed gaseous by-products will help to accelerate the formation rate of biuret.

[0028] In an optional embodiment of the method according to the present disclosure, the gas mixture is discharged from one or more reactor vessels via a pipeline to a scrubber configured to purify the gaseous by-products from the gas mixture to produce a purified gas. The scrubber more particularly uses water and / or an acid as the scrubbing liquid.

[0029] In an additional embodiment of the method according to the present disclosure, the method further comprises the following steps - purging a portion of the purified gas from the scrubber, which portion is a reusable gas fraction,

[0030] - compressing the reusable gas fraction to a pressure above atmospheric pressure and returning the pressure above atmospheric

[0031] pressure

[0032] gas fraction,

[0033] - compressing the reusable gas fraction to a pressure above atmospheric pressure and

[0034] Additional gas fractions of the pressure are added to the reusable gas fraction, or additional gas fractions are added to the reusable gas fraction and compressed to a pressure above atmospheric pressure

[0035] ; and

[0036] - Recycle the mixture of the additional gas fraction and the reusable gas fraction back to one

[0037] or more reactor vessels, particularly as a carrier gas and / or purge gas stream.

[0038] The pressure of the reusable gas fraction and the additional gas fraction (or fresh gas) is more particularly between 1 bar and 5 bar. The pressure should be such that there is a driving force for the gas mixture to flow from the reactor vessel to the scrubber.

[0039] In a possible embodiment of the method according to the present disclosure, a stirrer or agitator is used to stir the urea melt in the respective reactor vessel (i.e., the starting urea melt, which is converted into a melt containing urea, biuret, and N-containing compounds, and whose composition changes during the condensation process).

[0040] In the context of the present application, the circulation in the circulation loop is obtained via a circulation pumping device. The circulation pumping device can be designed such that the circulation in and out of the circulation loop arranged outside each of the reactor vessels is sufficient to mix the melt in the reactor vessels. However, the stirrer or agitator enhances the mixing process.

[0041] In a specific embodiment of the method according to the present disclosure, considering the weight of the total composition of the produced melt and the total composition forming 100 wt.%, the produced melt contains

[0042] - Urea between 5 wt.% and 60 wt.%, more particularly between 30 wt.% and 55 wt.%

[0043] of urea;

[0044] - Biuret between 2 wt.% and 60 wt.%, more particularly between 30 wt.% and 50 wt.%

[0045] of biuret; and

[0046] - N-containing compounds between 6 wt.% and 16 wt.%.

[0047] In a specific embodiment of the method according to the present disclosure, considering the weight of the total composition of the produced melt, the N-containing compounds contain

[0048] - Between 3 wt.% and 10 wt.%, more particularly between 5 wt.% and 8 wt.% or at 5

[0049] cyanuric acid between 1 wt.% and 7 wt.%,

[0050] - between 0.5 wt.% and 3 wt.%, more particularly between 0.8 wt.% and 2.0 wt.% or between

[0051] 0.8 wt.% and 1.5 wt.% of melamine, and

[0052] - between 3 wt.% and 6 wt.%, more particularly between 4 wt.% and 5.5 wt.% or between 4

[0053] wt.% and 5 wt.% of biuret.

[0054] In a particular embodiment of the method according to the present disclosure, the method further comprises the steps of - conveying the produced melt comprising urea, biuret and N-containing compounds from the respective reactor vessel

[0055] to a mixing vessel, and

[0056] - adding one or more animal feed supplement compounds to the melt comprising urea, biuret and N-containing compounds in the mixing vessel and mixing to obtain a feed supplement melt.

[0057] One or more animal feed supplement compounds are one or more of nitrate compounds, phosphate compounds, sulfate compounds, micronutrients and anti-caking agents.

[0058] More particularly, one or more feed supplement compounds are one or more nitrate compounds.

[0059] In a possible embodiment of the method according to the present disclosure, considering the total composition of the produced melt, one or more nitrate compounds are present in an amount between 20 wt.% and 40 wt.%.

[0060] More particularly, one or more nitrate compounds are selected from calcium nitrate, magnesium nitrate, ammonium nitrate, potassium nitrate, sodium nitrate or mixtures thereof.

[0061] In a specific embodiment of the method according to the present disclosure, the urea melt present in one or more reactor vessels is subjected to a heating process to obtain a melt of urea, biuret and N-containing compounds, the temperature of which is between 150 °C and 180 °C, more particularly between 160 °C and 170 °C, and most particularly 165 °C.

[0062]

[0063] ​Due to the complex digestive system of ruminants, which is characterized by a four-chambered stomach that allows for the efficient digestion of plant material by the microbiota in the stomach, ruminants are able to process both true protein and non-protein nitrogen (NPN) from their feed. It is well known that feed-grade urea is a source of NPN and rapidly decomposes in the ruminant body, releasing nitrogen in the form of ammonia to potentially toxic levels. Biuret provides a slower rate of ammonia release for rumen bacteria. Compared to urea, biuret is less toxic and is therefore safer to use in ruminant feed. However, the production of biuret is very expensive. Thus, the production method according to the present disclosure provides a melt that is more suitable for safer use in animal feed compared to pure urea.

[0064] According to a second aspect of the present disclosure, there is provided a system for producing a melt comprising urea, biuret, and a small amount of N-containing compounds produced during the urea condensation process. The system includes - pumping means for pumping a urea melt into one or more reactor vessels, each reactor vessel having a headspace at its top and a bottom, wherein the one or more reactor vessels are configured to produce the melt, and wherein each of the reactor vessels includes

[0065] · heating means configured to heat the urea melt to a temperature between 150°C and 180°C, wherein during the heating process, the urea melt is converted into a melt comprising urea, biuret, and N-containing compounds; and

[0066] · a circulation loop arranged outside the reactor vessel, the circulation loop comprising circulation pumping means to circulate the melt into and out of the corresponding reactor vessel via the circulation loop; and

[0067] · valves arranged to discharge gaseous by-products produced during the urea condensation process from the corresponding reactor vessel via the top of the corresponding reactor vessel; and

[0068] · valves arranged to remove the melt from the one or more reactor vessels at the bottom of the one or more reactor vessels.

[0069] The system is a compact system that requires a minimum number of components to obtain a melt comprising urea, biuret, and a small amount of N-containing compounds produced during the urea condensation process.

[0070] In an optional embodiment of the system according to the present disclosure, the circulation loop has an inlet opening and an outlet opening, wherein the circulation loop is connected to the reactor vessel, wherein the outlet opening is arranged as a narrow orifice, particularly wherein the inlet opening has the same diameter as the diameter of the circulation loop, and wherein the diameter of the outlet opening is smaller than the diameter of the circulation loop. This further improves the flashing of the melt.

[0071] ​

[0072] In a possible embodiment of the system according to the present disclosure, the system further comprises: a valve configured to introduce a carrier gas into a melt present in one or more reactor vessels, and a gas distributor disposed in the reactor vessels, wherein the carrier gas will then mix with the gaseous by-products to produce a gas mixture. The carrier gas may more particularly be nitrogen, carbon dioxide, air or a mixture thereof that is bubbled in the respective reactor vessels using the gas distributor.

[0073] In another possible embodiment of the system according to the present disclosure, the system further comprises a first gas purge device configured to introduce a purge gas stream into the headspace of one or more reactor vessels, wherein the purge gas stream will then mix with the gaseous by-products to produce a gas mixture. The purge gas stream is more particularly a purge air stream.

[0074] In an optional embodiment of the system according to the present disclosure, the system further comprises a scrubber configured to purify the gaseous by-products from the gas mixture to produce a purified gas. The scrubber more particularly uses water and / or acid as the scrubbing liquid.

[0075] In a possible embodiment of the system according to the present disclosure, the system further comprises - a second purge device for purging a portion of the purified gas from the scrubber, the

[0076] portion being a reusable gas portion,

[0077] - a compressor for pressurizing the reusable gas portion to above atmospheric pressure,

[0078] - a valve configured to add fresh

[0079] gas at a pressure above atmospheric pressure to the reusable gas portion, and

[0080] - a valve configured to recycle the mixture of fresh gas and reusable gas portion

[0081] back to one or more reactor vessels.

[0082] In a particular embodiment of the system according to the present disclosure, each of the reactor vessels may further comprise a stirrer, more particularly a mixer, configured to stir the melt in the respective reactor vessel.

[0083] In an optional embodiment of the system according to the present disclosure, the system includes a valve for removing a melt containing urea, biuret, and N-containing compounds from one or more reactor vessels, and further includes a pipeline for transporting the resulting melt containing urea, biuret, and N-containing compounds from one or more reactor vessels into a mixing vessel.

[0084] The system according to the present disclosure may further include a metering system for adding one or more nitrate compounds (in solid or liquid form) to the melt in the mixing vessel, and a mixing device for mixing the one or more nitrate compounds with the melt in the mixing vessel.

[0085] A specific embodiment of the system according to the present disclosure is configured to perform the method according to the present disclosure as described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0086] Figure 1 A flowchart showing a method for producing a melt according to the present disclosure, the melt containing urea, biuret, and a small amount of N-containing compounds generated during the urea condensation process;

[0087] Figure 2 A flowchart showing a method for producing a melt according to the present disclosure, the melt containing urea, biuret, a small amount of N-containing compounds generated during the urea condensation process, and one or more nitrate compounds. DETAILED DESCRIPTION

[0088] The present disclosure relates to the production of a melt of urea, biuret, and a small amount of N-containing compounds generated during the urea condensation process. The condensation of the starting urea source is obtained by applying it to a heating process. When urea is heated, starting from a temperature of approximately 132°C - 133°C, urea is converted into biuret and forms "by-products" (also known as "self-condensation products") in the form of N-containing compounds. The main N-containing compounds formed during the condensation process of urea are ammelide, cyanuric acid, and cyanuric triamide. The amount of N-containing compounds formed by the urea condensation process according to the present disclosure is present only in a "small" amount, i.e., up to 10 wt.% of the total resulting melt. As used herein, the term "urea melt" refers to the starting urea source as further discussed below, which is provided to the reactor vessel before being converted during the heating process. As used herein, the term "melt containing urea, biuret, and N-containing compounds" generally refers to the output product stream of the reactor vessel and corresponds to the resulting melt obtained after the condensation of the urea melt. As used herein, the term "urea-containing melt" or "melt in the reactor vessel" generally refers to the melt in the reactor vessel that is subjected to a heating process and has a continuously changing composition due to the ongoing condensation reaction.

[0089] In the production method according to the present disclosure, the urea melt is pumped by a pump into one or more reactor vessels in which the condensation process will occur. The urea melt supplied to the one or more reactor vessels particularly includes urea in the range of 95 wt.% to 100 wt.%. The urea melt can be sourced from different sources. The first option is to directly withdraw it from a urea production facility at an appropriate temperature and concentration. The second option is to directly withdraw it from the production facility at an appropriate temperature but in a more diluted form (or solution). The concentration of the urea melt withdrawn from the production facility varies depending on the location from which it is withdrawn. Typical concentrations of urea sourced from urea production facilities are 80 wt.%, 95 wt.%, or 99 wt.% urea. Urea with a concentration of 80 wt.% needs to have its concentration increased by evaporating water. Urea with concentrations of 95 wt.% and 99 wt.% can be directly used as the urea melt in the method according to the present disclosure. The third option is to melt solid urea.

[0090] Then, the urea melt is heated in the one or more reactor vessels to the required process temperature between 150 °C and 180 °C using a heating device, at which temperature the condensation reaction of urea occurs, producing biuret and N-containing compounds as described above. More particularly, the melt in the one or more reactor vessels is heated to a temperature between 160 °C and 170 °C, and most particularly to a temperature of 165 °C. It has surprisingly been found that this process temperature range produces a melt containing urea, biuret, and N-containing compounds, the ratio of urea:biuret:N-containing compounds being particularly effective when the melt is solidified and used as a non-protein nitrogen (NPN) feed supplement source for ruminants.

[0091] A single reactor vessel or a series of different reactor vessels can be provided. Each of the reactor vessels has a top with a headspace and a bottom. Any moisture present in the melt is evaporated by the heat and evaporates into the air present in the headspace of the corresponding reactor vessel. In these reactor vessels, the main formation of biuret and the formation of N-containing compounds occur, ultimately producing the melt required according to the present disclosure.

[0092] The method according to the present disclosure can be a batch system or a continuous system. In a batch system, the formation of the melt in the one or more reactor vessels takes place over a period of between 40 and 120 minutes, more particularly between 60 and 90 minutes, depending on the amount of melt present in the reactor vessels and the process conditions (mainly temperature). The typical residence time of the melt in the one or more reactor vessels is about 60 minutes. In a continuous system, the residence time of the melt generally occurs between 40 minutes and 60 minutes, depending on the flow rate of the melt through the reactor vessels and the volume of the reactor vessels.

[0093] During the heating process and the formation of the melt containing urea, biuret, and N-containing compounds, gaseous by-products are also generated. More particularly, since urea begins to degrade, at temperatures above the melting point of urea (about 132 °C), ammonia (NH 3 ) is mainly released. In addition, CO 2 (carbon dioxide) and H 2 O water vapor are also formed. Most of them are generated during the initial heating of urea. To increase the conversion rate of urea to biuret and N-containing compounds, the first possibility is to introduce a carrier gas into the melt present in one or more reactor vessels and then strip the gaseous by-products out of the reactor vessels. Thus, the carrier gas is mixed with the gaseous by-products to produce a gas mixture. The second possibility is to introduce a purge gas stream into the headspace of one or more reactor vessels, and this purge gas stream will then mix with the gaseous by-products to produce a gas mixture. These two options can also be carried out simultaneously or alternately.

[0094] Introducing a carrier gas into the melt present in one or more reactor vessels is more particularly carried out using a distributor that is designed to bubble the carrier gas from the bottom of the corresponding reactor vessel upwards into the melt. The carrier gas can be nitrogen, carbon dioxide, air, or a mixture thereof.

[0095] Introducing a purge gas stream into the headspace of one or more reactor vessels is more particularly accomplished by applying a purge air stream.

[0096] Then, the above-mentioned resulting gas mixture is discharged from the corresponding reactor vessel via the top of the corresponding reactor vessel. Optionally, the generated gas is discharged to a scrubber that is configured to wash out the gaseous by-products from the gas mixture, and a purified gas is obtained through this scrubber. The scrubber more particularly uses water and / or an acid, such as sulfuric acid (H 2 SO 4 ) or nitric acid (HNO 3 ) as the scrubbing liquid. More specifically, the scrubber is an ammonia scrubber that uses an acid to wash out the ammonia from the gas mixture discharged from the top of the corresponding reactor vessel.

[0097] The scrubber typically operates in a vacuum (i.e., at a pressure less than 1 bar). The pressure in the headspace of one or more reactor vessels should be higher than the pressure in the scrubber such that gas should flow from the one or more reactor vessels to the scrubber. The pressure in the headspace of one or more reactor vessels is typically atmospheric pressure. When bubbling gas is introduced into the melt present in a reactor vessel at a pressure above atmospheric pressure, the bubbling gas will expand in the headspace of the corresponding reactor vessel. There is a pipeline between the scrubber and the one or more reactor vessels. Optionally, a steam ejector is arranged in the pipeline to help reduce the pressure towards the scrubber. After the scrubber, a blower is typically provided which is configured to suck the gas out of the scrubber.

[0098] To avoid the accumulation of unwanted gaseous by-products such as nitrogen, the method further comprises the steps of

[0099] - purging a portion of the purified gas from the scrubber, which portion is a reusable gas

[0100] portion;

[0101] - compressing the reusable gas portion to a pressure above atmospheric pressure and adding fresh gas at a pressure above atmospheric pressure to the reusable gas portion, or adding fresh gas to the reusable gas

[0102] portion and compressing it to a pressure above atmospheric pressure; and

[0103] - recycling the mixture of fresh gas and reusable gas portion back to the one or more

[0104] reactor vessels.

[0105] The one or more reactor vessels are further provided with a circulation loop which is arranged outside the respective reactor vessel and is configured to circulate the melt through the circulation loop, wherein the melt flows from the reactor vessel into the circulation loop via an inlet opening of the circulation loop and back into the reactor vessel via an outlet opening of the circulation loop. This allows the melt present in the one or more reactor vessels to be mixed and contributes to mass transfer. The circulation loop is optionally heated to avoid blockage of the loop that may occur when the melt crystallizes in the loop. Suitable circulation pumping means are provided. For example, the circulation loop may be equipped with suitable circulation pumping means which are typically located in the vicinity of the reactor vessel to circulate the melt from the reactor vessel through the circulation loop and back into the reactor vessel. Advantageously, as is known to those skilled in the art, the circulation pumping means may be selected or configured to have the ability to ensure optimized or maximized mixing of the melt in the reactor vessel. Optionally, the circulation loop may be equipped with an ejector or eductor to further enhance the mixing of the melt in the reactor vessel. Advantageously, the circulation of the melt promotes the separation of gaseous by-products via flash evaporation. When the melt is circulated through the circulation loop by the circulation pumping means, the melt is pressurized. During the circulation of the melt in the circulation loop, due to heating, the melt further reacts with its self-condensation products. When the melt flows back into the respective reactor vessel, gases (especially ammonia) generated during the condensation reaction of the melt are released due to the pressure drop generated when the melt flows through the outlet opening of the circulation loop in the reactor vessel. In an optional embodiment, the outlet opening of the circulation loop (i.e., the location where the circulation loop is connected to the reactor vessel and where the melt flows out of the circulation loop into the respective reactor vessel) may be arranged as a narrow orifice to further promote the accumulation of the pressure of the melt and the subsequent expansion of the flow, in particular providing better separation of the gaseous by-products and the melt, or in other words, improving the flash evaporation of the melt. In other words, in certain embodiments, the circulation loop has an inlet and an outlet opening, wherein the circulation loop is connected to the reactor vessel, wherein the outlet opening is arranged as a narrow orifice, wherein the diameter of the inlet opening has the same size as the diameter of the circulation loop, and wherein the diameter of the outlet opening is smaller than the diameter of the inlet opening and smaller than the diameter of the circulation loop. Thus, in a particular embodiment, the separation of the gaseous by-products from the urea-containing melt further comprises flash evaporating the urea-containing melt during the circulation process, wherein the urea-containing melt is circulated back into the respective reactor vessel via the outlet opening formed in the circulation loop, the outlet opening being adapted to form a flow-limiting section in the circulation loop.

[0106] To enhance the mixing of the melt present in one or more reactor vessels, stirrers can be provided. More particularly, the stirrer is a mixer that can be used to achieve a good mixing effect. The reactor vessel can be a continuously stirred reactor vessel tank (CSTR). If two such CSTRs are placed in series, the size of the reactor vessel is reduced and proper mixing is ensured. More particularly, in this case, a CSTR with continuous gas bubbling is used.

[0107] After the desired melt is produced, the desired melt is removed from one or more reactor vessels via the bottom of one or more reactor vessels. The produced melt can be further processed into solid products by any known solidification technique.

[0108] Considering that the weight percentage is the weight of the total composition of the melt containing urea, biuret, and N-containing compounds and the total composition forms 100 wt.%, the produced melt obtained by the above process according to the present disclosure more particularly includes

[0109] - Urea between 5 wt.% and 60 wt.%, more particularly between 30 wt.% and 55 wt.%;

[0110] - Biuret between 2 wt.% and 60 wt.%, more particularly between 30 wt.% and 50 wt.%

[0111] between biuret; and

[0112] - N-containing compounds between 6 wt.% and 16 wt.%.

[0113] Considering that the weight percentage is the weight of the total composition of the produced melt containing urea, biuret, and N-containing compounds, the N-containing compounds more specifically include

[0114] - Cyanuric acid between 3 wt.% and 10 wt.%, more particularly between 5 wt.% and 8 wt.%,

[0115] - Cyanuric acid monoamide between 0.5 wt.% and 3 wt.%, more particularly between 0.8 wt.% and 2.0 wt.%; and

[0116] - Biuret between 3 wt.% and 6 wt.%, more particularly between 4 wt.% and 5.5 wt.%.

[0117] The produced melt can further include about 0.1 wt.% to 1.5 wt.% of water (based on the weight of the total composition of the melt).

[0118] Figure 1An example of a system for producing a melt containing urea, biuret, and a small amount of N-containing compounds generated during the urea condensation process according to the present disclosure and as described above is shown. The system (1) includes a pump (2) for pumping a starting urea melt to a preheater (3) configured to heat the starting urea melt to a temperature between 130 °C and 133 °C to obtain a urea melt. The urea melt is then pumped into a reactor vessel (4) where the urea melt undergoes a condensation reaction to produce a melt containing urea, biuret, and a small amount of N-containing compounds. The reactor vessel (4) has a top (4a) covering the top space (4b) and a bottom (4c). As already described above, it is also possible to provide a plurality of such reactor vessels (4) in series (not shown in the figure).

[0119] The reactor vessel (4) is arranged with a heater (not shown in the figure) configured to heat the melt to a desired reaction temperature between 150 °C and 180 °C, particularly between 160 °C and 170 °C, and more particularly about 165 °C.

[0120] The reactor vessel (4) further includes an agitator or mixer, such as an (eccentric) impeller or mixer (5), which is driven by a motor or other known type of drive (5a) and is configured to mix the melt present in the reactor vessel (4).

[0121] The reactor vessel (4) is also arranged with a circulation loop (7) extending to the outside, the circulation loop including inlet and outlet openings arranged with a pump (7a) for pumping the melt from the reactor vessel (4) into and through the circulation loop (7). The reactor vessel (4) of the exemplary system (1) is also provided with a circulation loop heater (7b) to heat the melt circulating through the circulation loop (7). The outlet of the circulation loop (7) may be adapted to restrict the flow of the melt in order to effect flashing of the melt.

[0122] A valve (not shown in the figure) is arranged at the bottom (4c) of the reactor vessel (4) to allow the produced melt to be withdrawn from the reactor vessel (4) for further processing.

[0123] The reactor vessel (2) is also provided with a gas distributor (6), more particularly nitrogen (N 2)A distributor configured to bubble a (nitrogen) gas from the bottom to the top of a reactor vessel (4) into a melt present in a reactor vessel (2). The gas distributor (6) more particularly has a circular bottom (6a) which also has perforations. The gas distributor (6) also has a vertically placed hollow tube (6b) configured to allow the (nitrogen) gas to flow through the hollow tube towards the bottom (6a). Nitrogen is injected to strip ammonia (NH 3 ).

[0124] The system (1) is also provided with a gas scrubber (10) for absorbing ammonia from a gas mixture of ammonia and nitrogen. The scrubber (10) uses water and / or an acid as a scrubbing liquid (8) to selectively absorb ammonia in the gas mixture, producing an aqueous ammonia solution. The aqueous ammonia solution leaves the scrubber at the bottom of the scrubber (9). In Figure 1 the exemplary system shown, a recirculation line (10) is provided to recirculate a portion of the aqueous ammonia solution back into the scrubber (9). The recirculation line (10) is provided with a pump (11) for pumping the aqueous ammonia solution from the bottom of the scrubber (9) back into the scrubber (9). The recirculation line (10) is also provided with a heat exchanger (12) for cooling the aqueous ammonia solution either before the aqueous ammonia solution is recirculated back into the scrubber (9) or before the aqueous ammonia solution is discharged from the system (1) through a drain pipe (13).

[0125] The gas leaving at the top of the scrubber (9) is rich in nitrogen. To avoid the accumulation of inert gases in the system (1), a valve (14) is used to purge a portion of the gas leaving the scrubber (9). The purged nitrogen-rich gas portion (only a small portion of the gas coming out of the scrubber (9)) is then compressed to above atmospheric pressure using a compressor (15) and mixed with fresh nitrogen in a mixer (16). Then the mixture is sent back and reused in the reactor vessel (4).

[0126] The method according to the present disclosure may also include the steps of: conveying a melt from a respective reactor vessel to a mixing vessel, adding one or more feed supplement compounds, more particularly one or more nitrate compounds, to the melt in the mixing vessel, and mixing, thereby obtaining a feed supplement melt. Thus, when a target percentage of biuret in the melt according to the present disclosure is obtained, one or more feed supplement compounds are more particularly added.

[0127] Considering the total composition of the feed supplement melt, the feed supplement melt obtained via the production method according to the present disclosure more particularly comprises one or more nitrate compounds between 20 wt.% and 40 wt.%, and more particularly about 30 wt.% of one or more nitrate compounds. These one or more nitrate compounds are more particularly selected from calcium nitrate, magnesium nitrate, ammonium nitrate, potassium nitrate, sodium nitrate or mixtures thereof.

[0128] Figure 2 An example of a system for producing a feed supplement melt is shown, which is based on a melt comprising urea, biuret and a small amount of N-containing compounds produced during the urea condensation process, as well as calcium nitrate as a nitrate compound.

[0129] The production method for producing the melt according to the present disclosure comprising urea, biuret and a small amount of N-containing compounds is the same as Figure 1 shown and described above. However, in Figure 2 , the melt having the required amounts of urea, biuret and N-containing compounds produced during the urea condensation process is pumped into a mixing vessel (17), which is configured to add calcium nitrate (18) to the melt and mix it using a mixer (19) driven by a motor (19a). The feed supplement melt is then withdrawn from the mixing vessel (17) for further processing.

Claims

1. A method for producing a melt comprising urea, biuret and N-containing compounds produced during the condensation of urea, the method comprising the following steps: - pumping a urea melt into one or more reactor vessels, each reactor vessel having a headspace at its top and a bottom, - subjecting the urea melt in the one or more reactor vessels to a heating process at a temperature between 150 °C and 180 °C, wherein during the heating process, the urea melt is converted into the melt comprising urea, biuret and N-containing compounds; wherein during the formation of the melt comprising urea, biuret and N-containing compounds, gaseous by-products are produced, and the gaseous by-products are discharged from the respective reactor vessel via the headspace of the respective reactor vessel; - removing the melt comprising urea, biuret and N-containing compounds from the one or more reactor vessels via the bottom of the one or more reactor vessels; characterized in that during the heating process, the melt present in the reactor vessel circulates in and out of the one or more reactor vessels via a circulation loop, wherein the circulation loop is arranged outside each of the reactor vessels and is equipped with a circulation pumping device.

2. The method according to claim 1, wherein the method is a batch method, and wherein the residence time of the melt in the one or more reactor vessels is between 40 minutes and 120 minutes, more particularly between 60 minutes and 90 minutes.

3. The method according to claim 1, wherein the method is a continuous method, and wherein the residence time of the melt in the one or more reactor vessels is between 40 minutes and 60 minutes.

4. The method according to any one of claims 1 to 3, wherein the method further comprises the following steps: - introducing a carrier gas into the melt present in the one or more reactor vessels, the carrier gas then mixing with the gaseous by-products to produce a gas mixture, the carrier gas being more particularly nitrogen, carbon dioxide, air or a mixture thereof bubbled in the respective reactor vessel using a gas distributor, and / or - introducing a purge gas stream into the headspace of the one or more reactor vessels, the purge gas stream then mixing with the gaseous by-products to produce a gas mixture, the purge gas stream being more particularly a purge air stream; and - discharging the gas mixture from the one or more reactor vessels via the top of the one or more reactor vessels.

5. The method according to claim 4, wherein the gas mixture is discharged from the one or more reactor vessels via a pipeline to a scrubber configured to purify the gaseous by-products from the gas mixture to produce a purified gas, wherein the scrubber more particularly uses water and / or acid as a scrubbing liquid.

6. The method according to claim 5, wherein the method further comprises the following steps: - purging a portion of the purified gas from the scrubber, the portion being a reusable gas fraction; - Compress the reusable gas fraction to a pressure above atmospheric pressure, and add an additional gas fraction at a pressure above atmospheric pressure to the reusable gas fraction, or add an additional gas fraction to the reusable gas fraction and compress it to a pressure above atmospheric pressure; And - Recycle the mixture of the additional gas fraction and the reusable gas fraction as the carrier gas and / or purge gas stream back to the one or more reactor vessels.

7. The method according to any one of claims 1 to 6, wherein during the formation of the melt containing urea, biuret and N-containing compounds in the respective reactor vessel, the melt in the respective reactor vessel is stirred, in particular using a stirrer.

8. The method according to any one of the preceding claims, wherein the total composition of the produced melt containing urea, biuret and N-containing compounds is considered by weight and the total composition forms 100 wt.%, and the produced melt containing urea, biuret and N-containing compounds contains - Urea between 5 wt.% and 60 wt.%, - Biuret between 2 wt.% and 60 wt.%, and - N-containing compounds between 6 wt.% and 16 wt.%.

9. The method according to claim 8, wherein considering the weight of the total composition of the produced melt containing urea, biuret and N-containing compounds, the N-containing compounds contain - Cyanuric acid between 3 wt.% and 10 wt.%, more particularly between 5 wt.% and 8 wt.%, - Cyanuric acid monoamide between 0.5 wt.% and 3 wt.%, more particularly between 0.8 wt.% and 2.0 wt.%; and - Cyanuric triamide between 3 wt.% and 6 wt.%, more particularly between 4 wt.% and 5.5 wt.%.

10. The method according to any one of the preceding claims, wherein the method further comprises the following steps: - Transfer the produced melt containing urea, biuret and N-containing compounds from the respective reactor vessel to a mixing vessel; And - Add one or more feed supplement compounds to the produced melt containing urea, biuret and N-containing compounds in the mixing vessel; And - Mix the produced melt containing urea, biuret and N-containing compounds with the one or more feed supplement compounds in the mixing vessel to obtain a feed supplement melt.

11. The method according to claim 10, wherein the one or more feed supplement compounds include one or more nitrate compounds.

12. The method according to claim 11, wherein considering the weight of the total composition of the feed supplement melt, the one or more nitrate compounds are present in an amount between 20 wt.% and 40 wt.%, more particularly, the one or more nitrate compounds are selected from calcium nitrate, magnesium nitrate, ammonium nitrate, potassium nitrate, sodium nitrate or a mixture thereof.

13. The method according to any one of the preceding claims, wherein the melt present in the one or more reactor vessels is subjected to a heating process to obtain a melt of urea, biuret and N-containing compounds having a temperature between 150 °C and 180 °C, more particularly between 160 °C and 170 °C and most particularly 165 °C.

14. A system for producing a melt comprising urea, biuret and N-containing compounds generated during the urea condensation process, the system comprising - pumping means for pumping a urea melt into one or more reactor vessels, each reactor vessel having a headspace at its top and a bottom, wherein the one or more reactor vessels are configured to produce therein the melt comprising urea, biuret and N-containing compounds, and wherein each of the reactor vessels comprises heating means configured to heat the urea melt to a temperature between 150 °C and 180 °C, wherein during the heating process the urea melt is converted into the melt comprising urea, biuret and N-containing compounds; and - valves arranged to discharge gaseous by-products generated during the urea condensation process from the respective reactor vessels via the headspace of the respective reactor vessels; and - valves arranged to remove the melt from the one or more reactor vessels at the bottom of the one or more reactor vessels, characterized in that each of the reactor vessels comprises a circulation loop arranged outside each of the one or more reactor vessels and comprising circulation pumping means for circulating the melt present in the one or more reactor vessels into and out of the respective circulation loop.

15. The system according to claim 14, wherein the circulation loop has an inlet opening and an outlet opening, wherein the circulation loop is connected to the reactor vessel, and wherein the outlet opening is arranged as a narrow orifice.

16. The system according to claim 14 or 15, wherein the system further comprises: a valve configured to introduce a carrier gas into the melt present in the one or more reactor vessels, and a gas distributor arranged in the reactor vessel, wherein the carrier gas will be mixed with the gaseous by-products to produce a gas mixture.

17. The system according to any one of claims 14 to 16, wherein the system further comprises a first gas purging means configured to introduce a purge gas stream into the headspace of the one or more reactor vessels, wherein the purge gas will be mixed with the gaseous by-products to produce a gas mixture.

18. The system according to claim 16 or 17, wherein the system comprises a scrubber configured to purify the gaseous by-products from the gas mixture.

19. The system according to claim 18, wherein the system further comprises - A second purge device for purging a portion of the purified gas, which is a reusable gas portion, from the scrubber. - A compressor for pressurizing the reusable gas portion to a pressure higher than atmospheric pressure. - A valve configured to add fresh gas having a pressure higher than atmospheric pressure to the reusable gas portion, and - A valve configured to recycle a mixture of the fresh gas and the reusable gas portion back to the one or more reactor vessels.

20. The system according to any one of claims 14 to 19, wherein each of the reactor vessels may further include a stirrer.

21. The system according to any one of claims 14 to 20, for performing the method according to any one of claims 1 to 13.

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